Hey welcome to the army that says no fellow menite
So some tips to get you to 50 points
You will only need one unit of choir as they all have to sing the same hymn unless you go jack heavy you will only need 2/3 of them at one time having 2/3 spare as they can be squishy,errant's are a good choice you'll need the u/a for them to give them quick work which is really handy..as for adding on menoth are very infantry heavy..
units wise,zealots and monalith bearer as a distraction/meat shield but for one turn they mini feat and turn invincible..the go to heavy hitters are bastions they have reach,weapon master and magic weapons and can spread there damage between them and cinerators wep masters and magic weps but instead of bastions damage management they get pissed when damaged which makes them faster and when they kill someone that person bursts into flames and can put others on fire..
solo's your must go too solos are rhupert the piper of ord or as most menoth players call him piper of menoth as we all use him all the time.he gives tough to a unit a turn which makes your errant's 10x harder to get rid of.
Bastion seneshal as he's a heavy hitter and heals your bastions a box per turn.
The covenant of menoth as he has nice denial's
High exemplar gravis as he is a hard hitter that makes all exemplar units immune to knockdown.errants,bastions and cinerators.
Jacks you have a good few to try out the now but I would highly recommend the blessing of vengeance jack as it's sevvys character Jack which adds +2 to attack and damage rolls for spells arced through him by sevvys this also includes the gun epic sevvy has.but is a good all round defence/offence or intercept jack
hope this helps